The present invention relates in general to the testing of pipes, and more particularly to method and apparatus for testing tubings and casings used in oilfield applications.
According to API Spec. 5A, Section 5.1, it is required that tubings and casings for oilfield applications and having a "power-tightened" threaded connecting sleeve of a diameter up to 133/8 inches (=339.7 mm), are required to undergo a hydraulic internal pressure test. For this purpose the tubings and casings, inclusive of the sleeve, are usually transported to a water-pressure testing machine, in which the entire assembly is filled with a water/emulsion mixture and pressurized to the required pressure level which must be maintained for a period of 5 seconds.
A problem with this approach is that it is quite elaborate and cost-intensive, since a complete water-circulation system must be installed. Another problem is that the brief five second time is not adequate to determine whether the threaded connection itself is actually tight, due to the fact that water dripping off the machine from the previously emptied pipe tends to obscure any leakage at the threaded joint. Moreover, if leakage does occur at the threaded joint, the quantity will be so small as to not cause any perceptible drop in the test pressure. Finally, the water-pressure testing machine itself is very expensive, especially because it must be connectable to both ends of the pipe and since both connecting heads of the machine must be capable of withstanding the quite enormous axial thrust of the pressurizing medium.
Also known in the prior art are methods and installations which make it possible to test a completed installation-ready connection of two oilfield pipes with external threaded connecting sleeve, either from the exterior (the Gather Hauck method) or from the interior at the site (in the drilling tower). However, both of these approaches can be used only in installation-ready applications. It is not possible to adapt either of these methods for use in factory (as opposed to on-site) testing, because after the completed test one of the two pipes would have to be unscrewed from the connecting sleeve which, as is known, usually results in a destruction of (or at least damage to) the threads involved.